diff --git a/include/c_interface.inc b/include/c_interface.inc
index 1d38b52b659e87c426c9768e87a2dcd2d9cdee5a..54eb9696657fc2e4e9df66ad192240775a262887 100644
--- a/include/c_interface.inc
+++ b/include/c_interface.inc
@@ -8,8 +8,8 @@ C
 
       double precision c_Mz
 
-      character*128 c_LHAPDF6OutDir
-      character*128 c_OutDirName
+      character*256 c_LHAPDF6OutDir
+      character*256 c_OutDirName
       character*128 c_LHAPDFSET
 
       double precision c_xgrid(NXGridMax)